A semiconductor power converter that converts a high voltage has a high voltage to ground. For this reason, a high cost is involved in satisfying the insulation property of semiconductor power converters, and such converters therefore have large volumes. In particular, to supply a gate driving voltage to switching elements having a high voltage to ground, it is necessary to provide a transformer having a high voltage to ground, to secure a fixed insulation distance. For this reason, it becomes difficult to supply a gate driving voltage to switching elements when the main circuit voltage of the semiconductor power converter exceeds 10 kV. When the gate power can be supplied from the main circuit, a switching element driving power supply circuit can be configured with a withstand voltage level for one switching element. This facilitates supply of a gate power. For this reason, the prior art includes a method for supplying the gate driving power to switching elements by dropping a voltage from the main circuit via a resistor.
In the conventional structure described above, the resistor of the power supply circuit has an increased loss due to Joule heat in comparison with the power supplied to the switching elements. This structure increases the volume of the resistor, and increases the standby power consumption of the power converter.